Random arrangement type silent chain

ABSTRACT

A random arrangement type silent chain restricting run-upon phenomenon to sprocket teeth to reduce contact noise at inner engagement surface and vibration noise of free span and restricting abnormal elongation and excessive load during power transmission, is provided. In the silent chain a first link plate, which begins to engage with the sprocket tooth by an inner crotch and sits on by an outer flank, and a second link plate, which engages with and sits on the sprocket tooth only by the outer flank, are mixed and combined endlessly in a chain longitudinal direction. A mixture ratio of the first link plates to the total link plates is set to less than 50% and at least one or more of the second link plates are randomly arranged before and after the first link plates. The run-upon phenomenon to the sprocket teeth is thus restricted.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates to a silent chain that includes a plate arrangement structure to reduce noise occurred when power is transmitted.

[0003] 2. Prior Art

[0004] Conventionally, a silent chain, which has been widely used for transmitting power between a crankshaft and a camshaft of an automobile engine, is combined by a large number of link plates on which crotched link teeth engaging with sprocket teeth are formed, and an outer engage surface or an inner engage surface of the crotched link tooth contacts the sprocket tooth to perform power transmission.

[0005] Various kinds of improvement has been made for such a silent chain to reduce noise occurred during power transmission. For example, the silent chain disclosed in Japanese Utility Model Publication No. 6-13399 adopts a link plate 1 whose inner engage surface 1 a is expanded at the center in a convex shape, and an inner engage surface 1 a of the link plate 1 that begins to engage with the sprocket tooth and another inner engage surface 1 a of the link plate 1 that engages with the sprocket tooth ahead of the former engage surface 1 a are made simultaneously contact adjacent sprocket teeth (s1, s2) of the sprocket. Thus, it is devised such that noise occurred during engagement of the teeth is dispersed to the adjacent sprocket teeth (s1, s2) of the sprocket and lightened.

[0006] However, in the silent chain described in the foregoing Japanese Utility Model Publication No. 6-13399, silent chain tension during power transmission and the tooth shape of the inner engage surface 1 a expanded in a convex shape cause excessive frictional force that interferes smooth contact in a sliding manner between the inner engage surface 1 a of the link plate 1 and the sprocket teeth (s1, s2). Then, the inner engage surface 1 a of the link plate 1 is caught by head portions of the sprocket teeth (s1, s2) to produce contact noise due to the frictional force, and a so-called run-upon phenomenon where the link plate 1 runs upon the head portions of the sprocket teeth (s1, s2) occurs as shown in FIG. 9.

[0007] An engage line of the silent chain in which the run-upon phenomenon has occurred is off from a sprocket pitch circle L3, which is an ideal engage line L1, by a run-upon width H in a head portion direction of the sprocket tooth in the case where the silent chain smoothly approaches the sprocket S to engage and sit thereon, and the run-upon width H is off by a larger amount as the inner engage surfaces 1 a of a plurality of the link plates 1 engage with a plurality of corresponding sprocket teeth (s1, s2, and so on) continuously and simultaneously. Accordingly, a silent chain traveling line L2 of a free span in a span state floats to cause too much play such as string vibration, which remarkably amplifies vibration noise.

[0008] Therefore, the conventional silent chain having the link plate 1 whose inner engage surface 1 a is expanded at the center in a convex shape has a problem that the contact noise of the inner engage surface 1 a newly occurred by the foregoing run-upon phenomenon and the vibration noise of the free span interfere a noise dispersion effect by the simultaneous contact of the inner engage surfaces la, and thus the effect cannot be exerted sufficiently. Furthermore, there has existed a problem that the foregoing run-upon phenomenon produced abnormal elongation and a large load on the link plate 1 to shorten a silent chain life remarkably.

SUMMARY OF THE INVENTION

[0009] The object of the present invention is to solve the foregoing problems of the prior art, and to provide a silent chain capable of reducing the contact noise of the inner engage surface and the vibration noise of the free span by restricting the run-upon phenomenon to the sprocket teeth and improving greatly the silent chain life by restricting abnormal elongation and the excessive load during power transmission.

[0010] A random arrangement type silent chain of the present invention is one in which a first link plate, which begins to engage with the sprocket tooth by an inner crotch and sits on by an outer flank, and a second link plate, which engages with and sits on the sprocket tooth only by the outer flank, are mixed and combined endlessly in a chain longitudinal direction. The foregoing problems are solved by setting a mixture ratio of the first link plates to the total link plates to less than 50% and by randomly arranging at least one or more of the second link plates before and after the first link plates.

[0011] Herein, the ‘inner crotch’ described in the present invention is the inner engage surface of the crotched link tooth formed on the link plate engaging with the sprocket tooth, and the ‘outer flank’ is the outer engage surface of the crotched link tooth.

[0012] The tooth surface shape of the inner crotch of the first link plate may be any of a curved shape that swells out a little when superposed on the outer flank (described later) of the second link plate, an arc shape and a shape in which these shapes are combined as long as the tooth surface has a shape in which the tooth can begin engagement with the sprocket tooth by the inner crotch. Further, the tooth surface shape of its outside may be any of a linear shape, a curved shape and a shape in which these are combined as long as the tooth surface has a shape in which the tooth sits on the sprocket tooth while sliding smoothly and avoiding striking noise.

[0013] Further, the tooth surface shape of the inner crotch of the second link plate may be any of a linear shape, a curved shape, an arc shape and a shape in which these shapes are combined as long as the tooth surface has a shape in which the inner crotch is not allowed to engage with the sprocket tooth, and the tooth surface shape of its outside may be any of a linear shape, a curved shape and a shape in which these shapes are combined as long as the tooth surface has a shape in which the tooth sits on the sprocket tooth only by the outer flank while sliding smoothly and avoiding striking noise.

[0014] Moreover, the first link plate and the second link plate adopted in the random arrangement type silent chain of the present invention may be either a link plate including pin holes for inserting connection pins or a link plate into which bushings for inserting the connection pins are fitted. Further, regarding the connection pins that combine the link plates endlessly, either of a round pin having a circular cross-section or a locker joint type pin in which rolling back surfaces of a locker pin and a joint pin face with each other may be adopted.

[0015] Note that a sprocket, with which the random arrangement type silent chain of the present invention engages, is a regular sprocket including a large number of uniform sprocket teeth, but a sprocket including sprocket teeth whose head portions are dropped out may also be used because it does not cause the run-upon phenomenon.

[0016] According to the random arrangement type silent chain of the present invention, by setting the mixture ratio of the first link plates to the total link plates to less than 50% and by randomly arranging at least one or more of the second link plates before and after the first link plates, the inner crotch of the first link plate does not engage with the sprocket teeth continuously and simultaneously even if any link plate in a chain longitudinal direction engages with the sprocket to cause an engagement pattern due to an arrangement mode of the link plates during power transmission, and thus the conventional run-upon phenomenon is restricted.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is an entire view of a random arrangement type silent chain being an embodiment of the present invention in the case where it is spanned on the sprocket.

[0018]FIG. 2 is an enlarged view of a first link plate used in this embodiment.

[0019]FIG. 3 is an enlarged view of a second link plate used in this embodiment.

[0020]FIG. 4 is a combination table of the first link plates and the second link plates in the random arrangement type silent chain of this embodiment.

[0021]FIG. 5 is a view showing a first engagement pattern A of this embodiment.

[0022]FIG. 6 is a view showing a second engagement pattern B of this embodiment.

[0023]FIG. 7 is a view showing a third engagement pattern C of this embodiment.

[0024]FIG. 8 is a table showing a noise measurement result between this embodiment and comparative examples.

[0025]FIG. 9 is a view showing a conventional engagement pattern.

PREFERRED EMBODIMENTS OF THE INVENTION

[0026] One embodiment of the present invention will be described in detail as follows with reference to the drawings. FIG. 1 is the entire view of the random arrangement type silent chain being the embodiment of the present invention in the case where it is spanned on the sprocket, FIG. 2 is the enlarged view of the first link plate used in this embodiment, and FIG. 3 is the enlarged view of the second link plate used in this embodiment. FIG. 4 is the combination table of the first link plates and the second link plates in the random arrangement type silent chain of this embodiment, in which a circle (◯) shows the link plate to be combined.

[0027] Accordingly, the random arrangement type silent chain of this embodiment shown in FIG. 1 is one in which the link plates 1 as shown in FIG. 2 and the second link plates 2 as shown in FIG. 3 are mixed in a chain longitudinal direction and combined by the connection pins 3, and at least one or more of the second link plates are randomly arranged before and after the first link plates.

[0028] Specifically, the silent chain of random arrangement type in this embodiment is the one in which the same link plates are arranged in a chain width direction and the mixture ratio of the first link plates to the total link plates to 33% and the first link plates are randomly arranged such that two or more of the plates are not continuously arranged.

[0029] The first link plate 1 having the crotched link tooth in FIG. 2 includes the inner crotch 1 a that functions at the starting time of engagement with the sprocket teeth and the outer flank 1 b that functions only when it engages with and sits on the sprocket teeth, the tooth shape of the inner crotch 1 a is in the arc profile expanded at the center in a convex shape when superposed on an outer flank 2 b (described later) of the second link plate 2 in a connected state, and the tooth shape of the outer flank 1 b is in the linear profile in which the tooth sits on the sprocket tooth while sliding smoothly and avoiding striking noise. Note that the virtual line in FIG. 2 shows an external profile in the case where the second link plate 2 is superposed on the first link plate 1 in the connected state.

[0030] The second link plate 2 having the crotched link teeth in FIG. 3 includes: an inner crotch 2 a that does not function at all in engagement with the sprocket teeth; and the outer flank 2 b that functions when it engages with and sits on the sprocket teeth, the tooth shape of the inner crotch 2 a has a profile such that it does not protrude from the outer flank 1 b of the first link plate 1 when superposed on the outer flank 1 b in the connected state, and the tooth shape of the outer flank 2 b is in the linear profile in which the tooth sits on the sprocket tooth while sliding smoothly and avoiding striking noise. Note that the virtual line in FIG. 3 shows an external profile in the case where the first link plate 1 is superposed on the second link plate 2 in the connected state.

[0031] Next, the random arrangement type silent chain of this embodiment has the following engagement patterns in the case where the mixture ratio of the first link plates 1 to the total link plates is set to 33%, the first link plates 1 and the second link plates 2 are randomly arranged such that two or more of the first link plates 1 are not continuously arranged in a chain longitudinal direction, and the silent chain is engaged with the sprocket with thirty-eight teeth as shown in FIGS. 1 and 4.

[0032] (1) First Engagement Pattern A

[0033] In this pattern, when the second link plate 2 engages with the sprocket after the first link plate 1 as shown in FIG. 5, the inner crotch 2 a of the second link plate 2 (the fourth link plate from the left in FIG. 5), which follows the first link plate 1, does not engage with the sprocket tooth s2 that follows the sprocket tooth s1 in the state where the inner crotch 1 a of the first link plate 1 (the third link plate from the left in FIG. 5) is engaged with the sprocket tooth s1. Accordingly, the contact noise caused by the inner crotch 2 a of the second link plate 2 does not occur at all. Moreover, since the conventional run-upon phenomenon is restricted to a run-upon width of about h1 on the second link plate 2 and the outer flank 2 b of the second link plate 2 is substantially restricted until it engages with the sprocket tooth s2 that follows the sprocket tooth s1, the engagement line does not go off greatly from the sprocket pitch circle toward the tooth head direction of the sprocket tooth.

[0034] (2) Second Engagement Pattern B

[0035] In this pattern, when the first link plate 1 engages with the sprocket after the second like plate 2 as shown in FIG. 6, the outer flank 2 b of the first link plate 1 (the second link plate from the left in FIG. 6) engages with the sprocket tooth s1 and the second link plate 2 (the third link plate from the left in FIG. 6) that follows the first link plate 1 is in a non-contact state with either the sprocket tooth s1 or the sprocket tooth s2, the inner crotch 1 a of the first link plate 1 (the fourth link plate from the left in FIG. 6) that follows the second link plate 2 engages with the sprocket tooth s2 that follows the sprocket tooth s1, and another inner crotch does not engage with the tooth continuously and simultaneously. Accordingly, the contact noise caused by another inner crotch does not occur at all. Moreover, since the conventional run-upon phenomenon is restricted to the run-upon width of about h2 on the second link plate 2, the engagement line does not go off greatly from the sprocket pitch circle toward the tooth head direction of the sprocket tooth.

[0036] (3) Third Engagement Pattern C

[0037] In this pattern, when the second link plate 2 engages with the sprocket after the second link plate 2 having the same shape as shown in FIG. 7, the outer flank 2 b of the second link plate 2 (the third link plate from the left in FIG. 7) having the same shape, which follows the second link plate 2, engages with the sprocket tooth s2 that follows the sprocket tooth s1 in the state where the outer flank 2 b of the second link plate 2 (the second link plate from the left in FIG. 7) is engaged with the sprocket tooth s1, but neither inner crotch 2 a of the second link plates 2 engages with the sprocket teeth (s1, s2). Accordingly, the contact noise caused by the inner crotch 2 a of the second link plate does not occur at all. Moreover, since the conventional run-upon phenomenon is restricted almost completely to the run-upon width of about h3, the engagement line barely goes off from the sprocket pitch circle toward the tooth head direction of the sprocket tooth.

[0038] Therefore, the random arrangement type silent chain of this embodiment forms any one of the foregoing three engagement patterns even if any part in a chain longitudinal direction engages with the sprocket during power transmission, because the first link plates 1 and the second link plates 2 are mixed and combined endlessly in a chain longitudinal direction. Thus, the conventional run-upon phenomenon is restricted all over the entire silent chain.

[0039] In the case where the foregoing random arrangement type silent chain of this embodiment is engaged with a sprocket having forty or more teeth, the link plates and the sprocket teeth produce a more complicated engagement pattern than the foregoing engagement patterns. However, it is unchanged that the inner crotch 1 a of the first link plate 1 does not engage with the sprocket continuously and simultaneously in any kind of complicated engagement pattern, and the conventional run-upon phenomenon is restricted all over the entire silent chain.

[0040] In the random arrangement type silent chain of this embodiment, which has been obtained as described, Table 1 of FIG. 8 shows a noise measurement result of order sound mainly caused by the contact noise and overall sound mainly caused by the vibration noise when the silent chain is engaged with the sprocket including regular uniform sprocket teeth and used in a regular revolution range of 1450 to 1800 r/min. In FIG. 1, this embodiment is the silent chain in which at least one or more of the second link plates 2 are randomly arranged and combined before and after the first link plates 1 (that is, the mixture ratio at 33%), a comparative example 1 is a silent chain in which the second link plates 2 used in this embodiment are combined continuously in a chain longitudinal direction (that is, the mixture ratio at 100%), a comparative example 2 is a silent chain in which at least one or more of the first link plates 1 are randomly arranged and combined before and after the second link plates 2 (that is, the mixture ratio at 67%), a comparative example 3 is a silent chain in which the first link plates 1 and the second link plates 2, which are used in this embodiment, are alternately combined in a chain longitudinal direction (that is, the mixture ratio at 50%), and a comparative example 4 is a silent chain in which the second link plates 2 used in this embodiment are continuously combined in a chain longitudinal direction (that is, the mixture ratio at 100%). Further, these comparative examples adopt a silent chain that has the total of eighty-four link plates in a chain longitudinal direction and in which the number of link plates in a chain width direction is the same, and the sprocket having thirty-five teeth are engaged, similarly to this embodiment. Note that P1 in Table 1 denotes the number of the first link plates 1 arranged in a chain longitudinal direction, P2 denotes the number of the second link plates 2 arranged in a chain longitudinal direction, and its mixture ratio is a percentage of P1/P1+P2.

[0041] As it is clear from Table 1 of FIG. 8, the order sound in the random arrangement type silent chain of this embodiment is 72.5 dB and the overall sound is 107.3 dB. Thus, the contact noise caused at the inner engage surface 1 a of the first link plate 1 and the vibration noise that is apt to occur by too much play on the silent chain traveling line L2 of the free span are reduced comparing to any of the comparative examples 1 to 4.

[0042] Moreover, according to the random arrangement type silent chain of this embodiment, the run-upon phenomenon to the sprocket teeth occurred in the conventional silent chain is restricted even if any part in a chain longitudinal direction engages with the sprocket S during power transmission. Accordingly, the silent chain of this embodiment exerts extensive effect such that the abnormal elongation and excessive load during power transmission are restricted to lengthen the silent chain life.

[0043] As described, according to the random arrangement type silent chain of the present invention, the inner crotch of the first link plate does not engage with the sprocket teeth continuously and simultaneously even if any link plate in a chain longitudinal direction engages with the sprocket to cause an engagement pattern due to an arrangement mode of the link plates during power transmission, because the mixture ratio of the first link plates, which begin to engage with the sprocket teeth by the inner crotch and sit by the outer flank, to the total link plates is set to less than 50%. Accordingly, the contact noise caused at the inner engagement surface of the first link plate can be reduced.

[0044] Furthermore, according to the random arrangement type silent chain of the present invention, the run-upon phenomenon to the sprocket teeth occurred in the conventional silent chain is restricted all over the entire silent chain even if any link plate in a chain longitudinal direction engages with the sprocket to cause an engagement pattern due to an arrangement mode of the link plates during power transmission, because one or more of the second link plates that engage with and sit on the sprocket teeth only by the outer flank are randomly arranged before and after the first link plates, which begins to engage with the sprocket teeth by the inner crotch and sits by the outer flank. Thus, slippage between the engagement line and the sprocket pitch circle becomes smaller and the vibration noise of the free span, which is in a span state between sprockets, can be reduced, and the abnormal elongation and the excessive load during power transmission can be reduced to lengthen the silent chain life remarkably. 

What is claimed is:
 1. A random arrangement type silent chain, comprising: a first link plate, which begins to engage with a sprocket tooth by an inner crotch and sits on by an outer flank; and a second link plate, which engages with and sits on said sprocket tooth only by the outer flank, in which the first link plates and the second link plates are mixed and combined endlessly in a chain longitudinal direction, wherein a mixture ratio of said first link plates to the total link plates is set to less than 50%, and at least one or more of said second link plates are randomly arranged before and after said first link plates.
 2. A random arrangement type silent chain according to claim 1 wherein a tooth surface shape of said inner crotch of said first link plate is any of a curved shape or an arc shape, or any combination of these shape, and a tooth surface shape of said outer flank of said first link plate is any of a curved shape or an arc shape, or any combination of these shape.
 3. A random arrangement type silent chain according to claim 1 wherein a tooth surface shape of said inner crotch of said second link plate is any of a curved shape or an arc shape, or any combination of these shape, and a tooth surface shape of said outer flank of said second link plate is any of a curved shape or an arc shape, or any combination of these shape.
 4. A random arrangement type silent chain according to claim 1 wherein said link plate for said first link plate and said second link plate is a link plate including pin holes for inserting connection pins or a link plate into which bushings for inserting the connection pins are fitted, and connection pin that combine said link plates endlessly is a round pin having a circular cross-section or a locker joint type pin in which rolling back surfaces of a locker pin and a joint pin face with each other may be adopted. 